1. Field of the Invention
The invention generally relates to devices, systems, and related methods for closing cardiac openings through tissue welding. An exemplary application of the invention can be found in closing a patent foramen ovale.
2. Background Information
The human heart is divided into four compartments or chambers. The left and right atria are located in the upper portion of the heart and the left and right ventricles are located in the lower portion of the heart. The left and right atria are separated from each other by a muscular wall, the intraatrial septum, while the ventricles are separated by the intraventricular septum.
Either congenitally or by acquisition, abnormal openings, holes, or shunts can occur between the chambers of the heart or the great vessels, causing blood to flow therethrough. Such deformities are usually congenital and originate during fetal life when the heart forms from a folded tube into a four chambered, two-unit system. The deformities result from the incomplete formation of the septum, or muscular wall, between the chambers of the heart and can cause significant problems.
One such deformity or defect, a patent foramen ovale, is a persistent, one-way, usually flap-like opening in the wall between the right atrium and left atrium of the heart. In the fetus, the foramen ovale serves as a conduit for right-to-left atrial shunting. After birth, with the establishment of pulmonary circulation, the increased left atrial blood flow and pressure results in functional closure of the foramen ovale. Normally, this is followed by anatomical closure of the two overlapping layers of tissue at the foramen ovale: the septum primurn and the septum secundum. However, in certain individuals, a patent foramen ovale (PFO) persists. Depending on the method used to detect a PFO, an estimated 25 to 35% of adults have PFO.
Because the left atrial pressure is normally higher than right atrial pressure, the flap in people with a PFO typically stays closed. However, under certain conditions, right atrial pressure exceeds left atrial pressure, creating the possibility for right to left shunting that can allow blood clots to enter the systemic circulation. Consequentially, paradoxical embolism via a PFO is being considered in diagnosing causes for ischemic strokes, especially in young patients. Many studies have confirmed a strong association between the presence of a PFO and the risk for paradoxical embolism or stroke. In addition, there is good evidence that patients with PFO and paradoxical embolism are at increased risk for future, recurrent cerebrovascular events.
Patients suffering a stroke or transient ischemic attack (TIA) in the presence of a PFO and without another apparent cause for ischemic stroke are considered for prophylactic medical therapy to reduce the risk of a recurrent embolic event. These patients are commonly treated with oral anticoagulants which have the potential for adverse side effects, such as hemorrhage, hematoma, and adverse interactions with other drugs. In certain cases, such as when anticoagulation is contraindicated, surgery may be used to close a PFO. Under direct visualization, a surgeon can suture together the septum secundum and septum primum with a continuous stitch.
Nonsurgical (i.e., percutaneous) closure of patent PFO, as well as other cardiac openings such as atrial septal defects and ventricular septal defects, have become possible using a variety of mechanical closure devices. Currently available closure devices, however, are often complex to manufacture and require a technically complex implantation procedure. Because they are mostly designed to close septal defects, which are actual holes different from the flap-like anatomy of PFO, the existing devices lack more specific anatomic conformability for closing PFO and other similar cardiac openings.
Improved devices, systems, and related methods for closing cardiac openings, such as PFO, are, therefore, needed.